During the majority of known diagnostic procedures, the diagnosis of the secondary air system does not take place, however, on the basis of acquired pressures, but on the basis of signals of a lambda sensor in the exhaust gas, which allows a calculation of the secondary air mass in the exhaust gas system. The disadvantage of this diagnostic possibility is, however, that a diagnosis after a cold start can only then be implemented if the lambda sensor has achieved its operational readiness, which is set at a certain operating temperature. The operational readiness especially in the case of turbocharged engines is achieved relatively late, because the lambda sensor is disposed as a rule in relatively cool exhaust gas behind the turbo charger. An additional disadvantage is that the mixing of the secondary air mass is dependent on the exhaust gas mass as well as on errors in the fuel metering, which result in an open loop control when the lambda sensor is not yet operationally ready. Moreover, future government standards (for example from the model year 2008 forward for California, USA) will allow a diagnosis affecting the exhaust gas to take place only during cold starting. This is especially critical for internal combustion engines with exhaust gas turbo chargers, because the operational readiness of the lambda sensor is under certain circumstances first achieved when a diagnosis is already no longer allowed.
Internal combustion engines with multiple groups of cylinders, for example V-engines with two banks of cylinders, have exhaust gas systems with sections, which carry the exhaust gas of the cylinder groups separated from each other. The secondary air is in the process fed into the separate sections, which requires secondary air feeds with separate secondary air valves. Due to government standards, errors in the separate secondary air feeds must be recognized as such and assigned to the affected secondary air feed.
Against this background the task of the invention lies in the designation of a procedure and a control unit, with which system errors in separate secondary air feeds are recognized and assigned to their respective feeds with the least possible outlay of hardware. The procedure should also especially be able to be implemented on turbocharged engines.